Yes, the CSL-300 device has two external antenna connectors. The images switch to 5GHz as long as there is a 5GHz dongle available. Future versions will also support to send on several WIFI cards. With that it would be possible to use 2.4GHz and 5GHz band at the same time for maximum robustness.

Yes, they should be straigt from the repo. Inside the images you can check the file “/home/pi/rpi_wifibroadcast_image_builder_version.txt” that contains the exact revision and any local changes that were used to build the image.

I tested the CSL-300 indoors and I got a range of 10m indoors with two thick brick walls in between. My guess would be that outdoors 100m should be possible. However, several people reported low range using these cards. So it seems that they are not perfect, at least for TX.